1. Field of the Invention
The present invention relates to a two-cycle internal combustion engine. A control valve is disposed in a communicating passage for communicating a combustion chamber with a chamber portion adjacent to the combustion chamber and for controlling the opening and closing of the communicating passage. A fuel or an air-fuel mixture is supplied into the combustion chamber through the communicating passage. In particular, the present invention relates to a two-cycle internal combustion engine having openings, such as fuel injection openings formed in a side wall of the cylinder at a position facing to the combustion chamber, configured to reduce the amount of air-fuel mixture or combustion gas that leaks from the combustion chamber into the crank chamber through gaps between the piston and the openings. This configuration of the combustion chamber avoids problems such as reduction in engine output or seizure of the piston due to local temperature rise.
2. Description of Background Art
Two-cycle internal combustion engines having scavenging is known. Air pre-compressed in a crank chamber and a rich air-fuel mixture formed in a chamber portion adjacent to a side of a combustion chamber is directly injected into the combustion chamber from a rich air-fuel mixture injection opening. A rich air-fuel mixture injection control valve disposed in a communicating passage for communicating the chamber portion to the combustion chamber is opened to inject the rich air-fuel mixture (see Japanese Patent Laid-open Nos. Sho 50-60617 and Hei 8-269366).
In this known engine, since scavenging is performed only by air containing no fuel pre-compressed in the crank chamber, blowby of an air-fuel mixture can be significantly reduced, resulting in a reduction of fuel consumption and an improvement in exhaust gas purifying performance. However, this known engine has a problem. As shown in FIG. 5, an opening height Ha of an opening 022 through which a rich air-fuel mixture is injected into a cylinder bore 05 is larger than a distance Hb between outermost side surfaces A and B in the direction of the cylinder axis, of a plurality of piston rings 029a and 029b. Accordingly, when these piston rings 029a and 029b pass through the opening 022, the air-fuel mixture and the combustion gas in the combustion chamber 013 leak into the crank chamber through a gap formed between the piston 06 and the opening 022. As a result, there is a reduction in engine output and possible seizure of the piston 06 due to local temperature rise.
Furthermore, the same problems occur when the opening height Ha of a highly compressed gas intake opening 027, opening into the combustion chamber 013, for allowing air in the combustion chamber 013 at a high pressure to transfer into a chamber portion 020 for forming a rich air-fuel mixture, is larger than the distance Hb between the outermost side surfaces A and B of the plurality of piston rings 29a and 29b in the direction of the cylinder axis.
In addition, reference numeral 04 indicates a cylinder head; 021 and 028 are communicating passages; 024 is a rich air-fuel mixture injection control valve (rotary valve); and 026 is a fuel injection device.